PRIDE IS SELF-LOVE, and in that sense a Christian is enjoined to be proud; another way of saying "Love your neighbor as yourself" is to say "Love yourself as your neighbor." That doesn't mean your pulse is supposed to quicken every time you look in the mirror any more than it's supposed to quicken every time your neighbor passes the window. It means simply that the ability to work for your own good despite all the less than admirable things you know about yourself is closely related to the ability to work for your neighbors' good despite all the less than admirable things you know about them. It also means that just as in this sense love of self and love of neighbor go hand in hand, so do dislike of self and dislike of neighbor. For example: (a) the more I dislike my neighbors, the more I'm apt to dislike myself for disliking them, and them for making me dislike myself, and so on; and (b) I am continually tempted to take out on my neighbors the dislike I feel for myself, just the way if I crack my head on a low door I'm very apt to kick the first cat, child, or chair unlucky enough to catch my bloodshot eye.
Self-love, or pride, is a sin when, instead of leading you to share with others the self you love, it leads you to keep your self in perpetual safe-deposit. You not only don't accrue any interest that way, but you become less and less interesting every day.